1. Field of the Invention
This invention generally relates to an engine. More particularly, this invention relates to an engine cylinder system where both distribution of fuel-air mixture in a combustion chamber and expelling of combusted gas from the combustion chamber are significantly improved.
2. Background Art
An internal combustion engine generally includes a cylinder or a cylinder block having a plurality of cylinders. It is known that highly turbulent or "instantly and evenly" distributed fuel-air mixture in the combustion chamber provides excellent engine performance including improved fuel consumption, power output and purification of exhausts.
A "lean-burn" combustion engine system is known, which burns "lean mixture." This lean-burn engine system consumes less fuel and thus can be more economical than a conventional gasoline engine system. The lean-burn engine system can lower contents of harmful carbon monoxide in exhausts. Lowering of nitric oxides can also be expected. However, ignition and burning of lean mixture at present is not as reliable as in the case with a conventional engine. One solution to this problem and other problems that the lean-burn system intrinsically possesses is "enhanced circulation" of fuel-air mixture within the combustion chamber so that the fuel-air mixture can be distributed within the combustion chamber "instantly" and "evenly."
FIG. 10 schematically shows a top view of a conventional engine cylinder 50 having a combustion chamber 51 to which a pair of inlet passages 52 and 53 are connected on the "same" side in fluid communication to feed fuel-air mixtures 56 and 57 into the combustion chamber 51. The inlet openings of the passages 52 and 53 open along the circumference of the cylinder 50 in an attempt to enhance the circulation of the fuel-air mixture. Similarly, a pair of exhaust passages 54 are connected to the combustion chamber 51 on the "same" opposite side in fluid communication to expel combusted gases from the combustion chamber 51.
It is noted that fuel may be premixed with air before entering the combustion chamber 51 (premixed fuel type), or may be injected directly into the combustion chamber 51 and mixed with air in the combustion chamber 51 (direct fuel injection type).
One of the inlet passages, passage 53 in this case, is internally provided with a fuel-air mixture control valve 55, generally a butterfly valve, which closes the passage 53 under control as shown in FIG. 9 for a low combustion load operation mode in order to restrain the gas flow 57, causing swirling 58 in the combustion chamber 51 as will be appreciated by a person skilled in the relevant art. This swirling 58 of the fuel-air gas flow 58 can improve combustion of the "thin" fuel-air mixture 56 in the chamber 51 partially through enhancement of the combustion velocity which shortens the combustion time, enhancing overall engine performance including purification of exhaust.
One important disadvantage of this conventional arrangement of the inlet and exhaust passages is that when such a butterfly valve 55 is fully open as shown in FIG. 10 for a high combustion load operation mode, the flow rates of the inlet gases 56 and 57 become substantially equal, which hinders swirling of the gases 56 and 57 in the combustion chamber 51, for the reverse directional flows of the gases 56 and 57 substantially interfere with each other in the combustion chamber 51, slowing and disrupting the distribution of the fuel-air mixtures 56 and 57 in the combustion chamber 51, as will be understood by a person skilled in the art. As a result, the combustion of the fuel in the combustion chamber 51 falls short of desired performance, resulting in less power output and more impurities than desired.
Another important disadvantage of not only this passage arrangement but also a single inlet, single exhaust passage type is that fuel-air mixture (premixed) or air (direct injection) is sucked into the combustion chamber from "one" side only and combusted gas is also expelled from "one" side only of the combustion chamber. As will be understood by a person skilled in the art, "the other" side of the combustion chamber is "far", and the farthest area in the combustion chamber will neither be "instantly" filled with fuel gas (fuel-air mixture) nor be "instantly" evacuated of combusted gas. As a result, the incoming gas and certain amount of outgoing gas will "coexist" in the combustion chamber, somehow deteriorating the burning performance in the combustion chamber.